External portable monitor wont work

I have a Dell PB14255, when trying to connect an external portable monitor trough usb c for both power and video with only one cable, it doesn’t work:

- I have enabled 15w output for usb c

- when using an external power source (even another usb A port of the laptop) video works

- monitor works on much older computers i own

- I think there must be a conflict with the Video alt display and power delivery, port can’t handle both

is there a solution to use my portable monitor with only one cable and no external power supply?